It is known to use certain magnesium dialkoxides as starting materials for the preparation of solid catalyst components for olefin polymerization, see for example U.S. Pat. No. 4,414,132, GB Pat. No. 1,554,340 and FR Pat. No. 2,324,652. Such preparation methods proceed via halogenation of the dialkoxide to form a magnesium dihalide by reaction with a suitable halogenating agent such as benzoylchloride, thionylchloride or titanium tetrachloride, and incorporation of an electron donor, e.g. ethyl benzoate. When halogenating agents other than a titaniumhalide are employed a further contacting with titanium halide ensures incorporation of the latter into the solid catalyst component in the required amount, usually 2 to 4.5% wt of titanium per gram of solid component.
Olefin polymerization catalyst components so produced can be satisfactory in terms of polymerization activity (polymer yield) and stereospecific performance (polymer isotactics content), however, a third important polymerization criterion, i.e. polymer morphology, leaves much room for improvement. In olefin polymerization polymer morphology is known to be a replica of catalyst morphology, and the Applicants have found that in catalyst components obtained from magnesium dialkoxides, the morphology of the catalyst component can be governed by the morphology of magnesium dialkoxide starting material. So, if one seeks to employ optimal catalyst morphology comprising spherical particles ideally, 5 to 25 micron diameter, it is desirable to avail of magnesium dialkoxide starting material having the same morphology.
While various grades of magnesium dialkoxides are available on the market, there is today no such commerical material having the desired optimal morphology. Applicants seek to provide a process for converting magnesium dialkoxides of whatever particle size or shape into spherical particles. It has already been proposed to achieve this by dispersing solid magnesium dialkoxide particles into a suitable liquid phase and to spray-dry the dispersion, c.f. DE No. 2,839,188. However, the spray-drying of dispersions is not attractive as the dispersed solid particles will tend to clog the fine orifices of the spray-drying equipment and to foul the pumping and metering systems.